A confocal imaging system (e.g., scanning laser opthalmoscope, confocal microscope, etc.) rejects light scattered from adjacent or out-of-plane voxels by use of a pinhole in front of the detector conjugate to the focal plane. This can improve image contrast and resolution over flood illumination and detection schemes. The line scanning approach multiplexes the illumination and detection in one dimension, while rejecting scattered light outside of the confocal range gate defined by the pixel size in a similar fashion as a flying-spot SLO.
Adaptive optics (AO) can be used as a tool to understand the structural and functional aspects of vision, the elegant but complex retinal circuitry, and the dissolution of that structure, wiring and processes during the execrable progression of disease. AO systems can sense ocular aberrations that arise primarily from the tear film, cornea, and lens with a wave-front sensor, and can corrects aberrations in a closed-loop manner with a wavefront compensator. A Hartmann-Shack wavefront sensor comprised of a lenslet array and CCD camera is typically used for rapid detection of ocular aberrations; however, other techniques such as interferometry can also be used. There are several methods to achieve wavefront correction including MEMS-based deformable mirrors, magnetic actuator deformable minors, and liquid crystal phase modulators.
AO can overcome limitations imposed by ocular geometry and optics. AO has enabled high lateral resolution imaging for clinical applications such as early detection, disease diagnosis and progression tracking. AO can be used as a tool to understand the structural and functional aspects of vision. These vision studies typically use improved imaging performance and some also benefit from improved ability to stimulate and probe retinal function. AO can also be used to guide therapies, for new drug discovery, and for the evaluation of therapeutic effectiveness. With AO, the fundamental level of information and detail that can be extracted from an eye is markedly improved.
The eye can essentially produce a nearly diffraction-limited retinal spot for a small pupil diameter less than approximately 2 mm. The eye has a numerical aperture (NA) of about 0.05 in this case and produces spots of 5 μm-10 μm for near-infrared light. However, as the pupil diameter is increased, ocular aberrations negate any gains from increased numerical aperture and the retinal spot size is essentially unchanged. A conventional confocal microscope can achieve sub-micron lateral (∝1/NA) and axial (∝1/NA2) resolution with the use of high numerical aperture (NA) objectives. In opthalmology, imaging the posterior segment is limited by the NA and aberrations of the eye (˜0.2 for a dilated pupil). Scanning laser opthalmoscopes (SLOs) are confocal instruments that block light scattered from other retinal lateral positions and depths that are not conjugate to a detector pinhole. They can achieve a lateral and axial resolution of approximately 5 μm-10 μm and 300 μm, respectively. The axial depth-of-focus for confocal instruments is often called the confocal range gate. AO can be used to correct ocular aberrations to achieve the true NA potential of a dilated eye. Adaptive Optics Scanning Laser Opthalmoscopes (AOSLOs) can achieve nearly diffraction limited spots (about 2.5 μm) and excellent optical sectioning (as low as 70 μm).
There are currently two barriers to widespread use of AO by clinicians and research scientists. The first barrier is the high cost of deformable mirrors. The second barrier is system complexity. Currently, AO systems can be built and operated only by researchers with extensive expertise in optics, engineering, and instrumentation. AO systems have been designed and constructed for the best imaging performance possible, to the exclusion of all other factors (size, cost, complexity, ease-of-use, etc.). This has slowed the transition of AO from the research lab to the clinic.